This invention relates to aircaft instrument systems.
With the increasing amount of air traffic there is a corresponding increasing risk of collision between two aircraft. Some aircraft already carry radar that are capable of identifying other aircraft within a certain range. The interpretation of radar images provided by such instruments is, however, difficuIt, especially in congested airspace and it may not be readily apparent whether a target aircraft is at the height and on a path that could result in a collision. The difficulty of interpeting such radar displays is increased by the other tasks which the aircrew have to perform, especially during landing and take-off maneuvers which generally take place where air traffic congestion is most severe.
If the pilot does identify a target aircraft on a collision course and takes evading action, this may not avoid danger if the pilot of the target aircraft also takes evading action of the kind that negates the action taken by the pilot of the first aircraft.
In order to reduce the risk of such collisions, it has been proposed that all aircraft carry a traffic alert and collision avoidance system (TCAS) that would alert the pilot of possible collision and advise him of what evading action, if any, he should take. The pilots of the two aircraft on a collision course would each be advised of evading action that would not conflict with evading action taken by the other pilot.
As previously proposed, the TCAS system would include a modified vertical speed indicator instrument (VSI) that would replace the conventional VSI. The modified VSI would have colored sectors movable around the dial of the instrument in such a way that the location of the sectors indicate to the pilot that he should climb, reduce height, maintain height or maintain/reduce his present rate of climb/descent. Such an instrument may function satisfactorily providing that it is watched carefully by the pilot. However, once alerted about a possible collision danger, the natural instinct of the pilot is to identify visually the colliding aircraft by looking through the cockpit window, rather than to look down at the instrument panel.